Flash Flood Warning 40, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
938 AM MST Wed Aug 16 2023

.SYNOPSIS...Monsoon moisture will remain over northern Arizona
through the week. Showers and thunderstorms are forecast to
develop each afternoon and evening. Deep tropical moisture should
arrive by the weekend. This will increase the chances of showers
and thunderstorms over northern Arizona Saturday and Sunday. Near
normal temperatures and light afternoon breezes will prevail
outside of showers and storms.

&&

.UPDATE...No changes to the forecast this morning. Focus has been
on the changing pattern with the coming weekend. The tropical
system we've been focusing on off the western Mexico coast has
been named: TS Hilary. Confidence is still low as to how much rain
and subsequently what impacts we will have here in northern
Arizona. Even ensemble based guidance has been shifting more
northward with the track over the past 24 hours. Despite this
shift, Arizona remains a no-mans-land between little to normal
rainfall and several inches of rain over multiple days. Some
limitations to the forecast besides just the track are cloud cover
and instability: if we get too much cloud cover Saturday from
thunderstorms the night before we could experience significantly
less rainfall since activity would be dramatically subdued.
That's a scenario currently projected by the GFS. Euro on the
other hand has much clearer sky conditions meaning we would have
more instability to work with. Sadly just lots of pieces to work
with right now that have different outcomes based on how they come
together.

&&

.PREV DISCUSSION /242 AM MST/...There really is no end in sight to
the flow of monsoon moisture across northern Arizona. High
pressure will remain centered east of Arizona, wobbling from over
New Mexico/Colorado to the central United States and then back
toward New Mexico/Colorado over the coming 6 to 10 days. At the
same time troughing will remain off the west coast helping to
produce a general moist southerly flow across Arizona. Toward the
weekend and lasting into next week very deep tropical moisture
will push into Arizona, especially western portions, where an
increased threat of flash flooding could become an issue.

For today and Thursday...Not much change in the current pattern.
Just about the same coverage and timing of showers and
thunderstorms as seen on Tuesday. The focus will once again be
from the White Mountains and Mogollon Rim westward to Yavapai
County and Grand Canyon country. The typical storm threats will
exist with cloud-to-ground lightning and locally heavy rain.
Otherwise, little change in temperatures and light breezes away
from thunderstorms.

Starting Friday and lasting into early next week...High pressure
will remain centered to the east of Arizona with a trough off the
west coast for a continuation of moist southerly flow. In fact,
the flow will tap deep into the tropics with a significant push of
moisture moving northward over the Gulf of California. Later in
the weekend, from Saturday into Sunday, this moisture push will be
helped along, by a so far unnamed, tropical system moving
northward along the Baja California coast. The main impact for
northern Arizona will be deep moisture and unstable air mass from
about a Payson to Winslow to Page line westward. It is across this
area where the potential for an increased flash flood event may
develop. Confidence remains on the lower side since there is still
some uncertainty as to where the plume of deepest moisture will
head (it could head into California and Nevada). The main point
is keep checking back as the weekend trends come more into focus.
East of the line described above storm activity will remain mainly
isolated. Winds could get a little gusty later in the weekend as
pressure gradients are expect to strengthen, partially in
response to the tropical system along the Baja California coast
and the very strong high pressure system to the east. Otherwise,
mainly seasonable temperatures through the period.

&&

.AVIATION...For the 18Z TAF Package...Expecting mostly VFR
conditions for the period. TS and SHRA has ended for the moment
across the area. Expecting widely scattered TS to redevelop after
19Z. Nearby TS will result in gusty outflow winds for sites this
evening. Activity will diminish after 3Z, but pockets of TS and SHRA
will linger overnight until ~12Z. Aviation discussion not updated
for TAF amendments.

&&

.FIRE WEATHER...Today and Thursday...Scattered showers and
thunderstorms will continue each afternoon/evening. Winds near
storms could be gusty and erratic. Otherwise, look for south-
southwest winds of 10-20 mph each afternoon. Minimum RH values
will range between 20-40%.

Friday through Sunday...Scattered showers and storms will continue
Friday, before more widespread coverage comes in over the weekend.
Flash flooding will be the biggest threat over the weekend,
primarily for susceptible areas in Coconino and Yavapai Counties.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...None.

&&

PUBLIC...RKR/McCollum
AVIATION...RKR
FIRE WEATHER...Konieczny

For Northern Arizona weather information visit
weather.gov/flagstaff

Special Weather Statement
National Weather Service Flagstaff AZ
1244 PM MST Wed Aug 16 2023

AZZ012-015-162015-
Little Colorado River Valley in Coconino County-Western Mogollon Rim-
1244 PM MST Wed Aug 16 2023

...A STRONG THUNDERSTORM WILL IMPACT PORTIONS OF US-89 IN COCONINO
COUNTY THROUGH 115 PM MST...

At 1243 PM MST, Doppler radar was tracking a strong thunderstorm near
Nalahiku Pueblo in Wupatki N.M., or 25 miles north of Flagstaff,
moving west at 5 mph.

HAZARD...Wind gusts up to 50 mph and half inch hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Nalahiku Pueblo in Wupatki N.M. and Wupatki National Monument.

This includes U.S. Highway 89 between mile markers 437 and 450.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 3561 11140 3544 11147 3549 11169 3570 11159
TIME...MOT...LOC 1943Z 103DEG 6KT 3557 11153

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...50 MPH

BAJ

Special Weather Statement
National Weather Service Flagstaff AZ
211 PM MST Wed Aug 16 2023

AZZ008-037-162145-
Yavapai County Valleys and Basins-Yavapai County  Mountains-
211 PM MST Wed Aug 16 2023

...A STRONG THUNDERSTORM WILL IMPACT PRESCOTT VALLEY IN YAVAPAI
COUNTY THROUGH 245 PM MST...

At 210 PM MST, Doppler radar was tracking a strong thunderstorm over
Antelope Park, or over Prescott Valley, moving north at 5 mph.

HAZARD...Wind gusts up to 40 mph and half inch hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Prescott Valley, Yavapai County Fairgrounds, Glassford Hill, Mountain
Valley Park, Prescott Mall, Antelope Park, Prescott Airport, Prescott
Gateway Mall, Fain Lake, Watson Lake, and Prescott Valley Event
Center.

This includes the following highways...
 State Route 89 between mile markers 317 and 318.
 State Route 89A between mile markers 318 and 329.
 State Route 69 between mile markers 285 and 294.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 3454 11228 3454 11242 3469 11243 3468 11223
TIME...MOT...LOC 2110Z 183DEG 6KT 3462 11233

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...40 MPH

BAJ